U.S. patent application number 13/324826 was filed with the patent office on 2013-05-09 for partitioning data within a distributed data storage system using virtual file links.
This patent application is currently assigned to SAP AG. The applicant listed for this patent is Ivan Schreter, Dirk Thomsen. Invention is credited to Ivan Schreter, Dirk Thomsen.
Application Number | 20130117528 13/324826 |
Document ID | / |
Family ID | 48224545 |
Filed Date | 2013-05-09 |
United States Patent
Application |
20130117528 |
Kind Code |
A1 |
Thomsen; Dirk ; et
al. |
May 9, 2013 |
Partitioning Data Within A Distributed Data Storage System Using
Virtual File Links
Abstract
A record within a destination virtual file is generated on a
destination node of a distributed data storage system. The record
comprises (i) a link directed to a partition of a source virtual
file stored on a source node and (ii) partition criteria
characterizing the partition. The source virtual file is mapped to
a chain of linked pages stored in a page buffer of the distributed
data storage system and the partitioning criteria is used by at
least one of the source node and the destination node to identify
data associated with the partition. A request is later received at
the destination node to access data defined by the destination
virtual file. Data is provided, in response to the request, from
the partition of the source virtual file stored on the source node
using the link and the partitioning criteria. Related apparatus,
systems, techniques and articles are also described.
Inventors: |
Thomsen; Dirk; (Heidelberg,
DE) ; Schreter; Ivan; (Malsch, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Thomsen; Dirk
Schreter; Ivan |
Heidelberg
Malsch |
|
DE
DE |
|
|
Assignee: |
SAP AG
Walldorf
DE
|
Family ID: |
48224545 |
Appl. No.: |
13/324826 |
Filed: |
December 13, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13290835 |
Nov 7, 2011 |
|
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13324826 |
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Current U.S.
Class: |
711/173 ;
711/E12.002 |
Current CPC
Class: |
G06F 16/188
20190101 |
Class at
Publication: |
711/173 ;
711/E12.002 |
International
Class: |
G06F 12/00 20060101
G06F012/00 |
Claims
1. A computer program product comprising a non-transitory
machine-readable medium storing instructions that, when executed by
at least one programmable processor, cause the at least one
programmable processor to perform operations comprising:
generating, on a destination node of a distributed data storage
system, a record within a destination virtual file, the record
comprising (i) a link directed to a source virtual file stored on a
source node and (ii) partition criteria characterizing a partition
of the source virtual file, the source virtual file being mapped to
a chain of linked pages stored in a page buffer of the distributed
data storage system, the partitioning criteria being used by at
least one of the source node and the destination node to identify
data associated with the partition; receiving, at the destination
node, a request to access data defined by the destination virtual
file; providing, in response to the request, data from the
partition of the source virtual file stored on the source node
using the link and the partitioning criteria; and dropping the
partition of the source virtual file after a new version of the
destination virtual file is persisted while maintaining other
portions of the source virtual file other than the partition.
2. A computer program product as in claim 1, wherein the operations
further comprise: appending data generated at the destination node
subsequent to the generation of the record to the record, the
appended data forming a delta log at the destination node.
3. A computer program product as in claim 2, wherein the operations
further comprise: overwriting the destination virtual file and the
delta log during a columnar table merge operation with the new
version of the destination virtual file comprising data from the
partition of the source virtual file and the delta log.
4. A computer program product as in claim 3, wherein the link in
the record is overwritten during the columnar table merge
operation.
5. A computer program product as in claim 3, wherein the operations
further comprise: persisting the new version of the destination
virtual file to secondary data storage.
6. A computer program product as in claim 5, wherein the new
version of the destination virtual file is persisted after a
savepoint on the destination node.
7. A computer program product as in claim 5, wherein the the new
version of the destination virtual file is persisted to the
secondary data storage.
8. A computer program product as in claim 7, wherein dropping the
partition of the source virtual file comprises ceasing log
operations relative to a portion of the source virtual file
corresponding to the partition.
9. A computer program product as in claim 8, wherein dropping the
partition of the source virtual file comprises deleting a portion
of the source virtual file corresponding to the partition.
10. A method comprising: generating, on a destination node of a
distributed data storage system, a record within a destination
virtual file, the record comprising (i) a link directed to a source
virtual file stored on a source node and (ii) partition criteria
characterizing a partition of the source virtual file, the source
virtual file being mapped to a chain of linked pages stored in a
page buffer of the distributed data storage system, the
partitioning criteria being used by at least one of the source node
and the destination node to identify data associated with the
partition; receiving, at the destination node, a request to access
data defined by the destination virtual file; providing, in
response to the request, data from the partition of the source
virtual file stored on the source node using the link and the
partitioning criteria; and dropping the partition of the source
virtual file after a new version of the destination virtual file is
persisted while maintaining other portions of the source virtual
file other than the partition.
11. A method as in claim 10, further comprising: appending data
generated at the destination node subsequent to the generation of
the record to the record, the appended data forming a delta log at
the destination node.
12. A method as in claim 11, further comprising: overwriting the
destination virtual file and the delta log during a columnar table
merge operation with the new version of the destination virtual
file comprising data from the partition of the source virtual file
and the delta log.
13. A method as in claim 12, wherein the link in the record is
overwritten during the columnar table merge operation.
14. A method as in claim 12, further comprising: persisting the new
version of the destination virtual file to secondary data
storage.
15. A method as in claim 14, wherein the new version of the
destination virtual file is persisted after a savepoint on the
destination node.
16. A method as in claim 14, wherein the the new version of the
destination virtual file is persisted to the secondary data
storage.
17. A method as in claim 16, wherein dropping the partition of the
source virtual file comprises ceasing log operations relative to a
portion of the source virtual file corresponding to the
partition.
18. A method as in claim 17, wherein dropping the partition of the
source virtual file comprises deleting the portion of the source
virtual file corresponding to the partition.
19. A system comprising: at least one data processor; and memory
coupled to the at least one data processor, the memory storing
instructions, which when executed, cause the at least one data
processor to perform operations comprising: generating, on a
destination node of a distributed data storage system, a record
within a destination virtual file, the record comprising (i) a link
directed to a source virtual file stored on at least two source
nodes and (ii) partition criteria characterizing a partition of the
source virtual file on one of the source nodes, the source virtual
file being mapped to a chain of linked pages stored in a page
buffer of the distributed data storage system, the partitioning
criteria being used by at least one of the source nodes and the
destination node to identify data associated with the partition;
receiving, at the destination node, a request to access data
defined by the destination virtual file; and providing, in response
to the request, data from the partition of the source virtual file
stored on the corresponding source node using the link and the
partitioning criteria; and dropping the partition of the source
virtual file after a new version of the destination virtual file is
persisted while maintaining other portions of the source virtual
file other than the partition.
20. A system as in claim 19, wherein the operations further
comprise: appending data generated at the destination node
subsequent to the generation of the record to the record, the
appended data forming a delta log at the destination node; and
overwriting the destination virtual file and the delta log during a
columnar table merge operation with the new version of the
destination virtual file comprising data from the partition of the
source virtual file and the delta log.
Description
RELATED APPLICATION
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 13/290,835 filed on Nov. 7, 2011, the contents
of which are hereby fully incorporated by reference.
TECHNICAL FIELD
[0002] The subject matter described herein relates to techniques
for partitioning data and enabling access to partitioned data
within a distributed data storage system using virtual file
links.
BACKGROUND
[0003] In a distributed data storage system, data containers
sometimes become so big that they must be partitioned/split over
several nodes due to memory limitations and/or performance issues.
Partitioning a data container means splitting a data container into
several parts as well as combining smaller data containers into a
single data container and moving associated data to another node.
With some conventional database systems, this requires not only
moving the data but also moving one or more logs tracking changes
to such data container. These operations can be processor intensive
and can also consume additional storage.
SUMMARY
[0004] In one aspect, a record is generated within a destination
virtual file on a destination node of a distributed data storage
system. The record comprises (i) a link directed to a source
virtual file stored on a source node and (ii) partition criteria
characterizing a partition of the source virtual file. The source
virtual file is mapped to a chain of linked pages stored in a page
buffer of the distributed data storage system. The partitioning
criteria is used by at least one of the source node and the
destination node to identify data associated with the partition.
Thereafter, a request is received at the destination node to access
data defined by the destination virtual file. In response to the
request, data is provided from partition of the source virtual file
stored on the source node using the link and the partitioning
criteria.
[0005] Data generated at the node subsequent to the generation of
the record can be appended to the record. The appended data can
form a delta log at the destination node. The destination virtual
file and the delta log can be overwritten during a columnar table
merge operation with a new version of the destination virtual file
comprising data from the partition of the source virtual file and
the delta log. The link in the record can be overwritten during the
columnar table merge operation. The new version of the destination
virtual file can be persisted to secondary data storage. The new
version of the destination virtual file can be persisted after a
savepoint on the destination node. The partition of the source
virtual file can be dropper after the new version of the
destination virtual file is persisted to the secondary data
storage. Dropping the partition of the source virtual file can
include ceasing log operations relative to a portion of the source
virtual file corresponding to the partition and/or deleting a
portion of the source virtual file corresponding to the
partition.
[0006] Articles of manufacture are also described that comprise
computer executable instructions permanently stored on
non-transitory computer readable media, which, when executed by a
computer, causes the computer to perform operations herein.
Similarly, computer systems are also described that may include a
processor and a memory coupled to the processor. The memory may
temporarily or permanently store one or more programs that cause
the processor to perform one or more of the operations described
herein. In addition, operations specified by methods can be
implemented by one or more data processors either within a single
computing system or distributed among two or more computing
systems.
[0007] The subject matter described herein provides many
advantages. For example, the current techniques allow for the
partitioning of data among nodes within a distributed data storage
system (i.e., a database system comprising a plurality of nodes,
etc.) with little performance impact. Using links to virtual files
as described herein obviates the need, during recovery from a log
backup, for moving a portion of a virtual file from one node to the
other which in turn requires writing a redo log on a destination
node for all moved data or explicit expensive synchronization of
recovery on several nodes. Stated differently, the use of a link to
a virtual file requires a single operation (reading the linked
virtual file) as opposed to physically moving data which requires
at least three operations (writing data from the virtual file to
the destination node, writing a log from the virtual file to the
destination node, and reading data written to the destination
node).
[0008] The details of one or more variations of the subject matter
described herein are set forth in the accompanying drawings and the
description below. Other features and advantages of the subject
matter described herein will be apparent from the description and
drawings, and from the claims.
DESCRIPTION OF DRAWINGS
[0009] FIG. 1 is a diagram illustrating a system including a data
storage application;
[0010] FIG. 2 is a process flow diagram illustrating partioning
data within a distributed data storage system using virtual file
links;
[0011] FIG. 3 is a diagram illustrating details of the system of
FIG. 1; and
[0012] FIG. 4 is a diagram illustrating partitioning of data on a
source node to a destination node within a distributed data storage
system.
[0013] Like reference symbols in the various drawings indicate like
elements.
DETAILED DESCRIPTION
[0014] FIG. 1 shows an example of a system 100 in which a computing
system 102, which can include one or more programmable processors
that can be collocated, linked over one or more networks, etc.,
executes one or more modules, software components, or the like of a
data storage application 104. The data storage application 104 can
include one or more of a database, an enterprise resource program,
a distributed storage system (e.g. NetApp Filer available from
NetApp of Sunnyvale, Calif.), or the like.
[0015] The one or more modules, software components, or the like
can be accessible to local users of the computing system 102 as
well as to remote users accessing the computing system 102 from one
or more client machines 106 over a network connection 110. One or
more user interface screens produced by the one or more first
modules can be displayed to a user, either via a local display or
via a display associated with one of the client machines 106. Data
units of the data storage application 104 can be transiently stored
in a persistence layer 112 (e.g. a page buffer or other type of
temporary persistency layer), which can write the data, in the form
of storage pages, to one or more storages 114, for example via an
input/output component 116. The one or more storages 114 can
include one or more physical storage media or devices (e.g. hard
disk drives, persistent flash memory, random access memory, optical
media, magnetic media, and the like) configured for writing data
for longer term storage. It should be noted that the storage 114
and the input/output component 116 can be included in the computing
system 102 despite their being shown as external to the computing
system 102 in FIG. 1.
[0016] Data retained at the longer term storage 114 can be
organized in pages, each of which has allocated to it a defined
amount of storage space. In some implementations, the amount of
storage space allocated to each page can be constant and fixed.
However, other implementations in which the amount of storage space
allocated to each page can vary are also within the scope of the
current subject matter.
[0017] FIG. 2 is a process flow diagram 200 in which, at 210, a
record is generated on a destination node of a distributed data
storage system. The record can include (i) a link directed to a
source virtual file stored on a source node and (ii) partition
criteria characterizing a partition of the source virtual file. The
source virtual file can be mapped to a chain of linked pages stored
in a page buffer of the distributed data storage system, the
partitioning criteria being used by at least one of the source node
and the destination node to identify data associated with the
partition. Subsequently, at 220, a request is received at the
destination node to access data defined by the destination virtual
file. In response to the request, at 230, data is provided from the
partition of the source virtual file stored on the source node
using the link and the partitioning criteria.
[0018] FIG. 3 shows a software architecture 300 consistent with one
or more features of the current subject matter. A data storage
application 104, which can be implemented in one or more of
hardware and software, can include one or more of a database
application, a network-attached storage system, or the like.
According to at least some implementations of the current subject
matter, such a data storage application 104 can include or
otherwise interface with a persistence layer 112 or other type of
memory buffer, for example via a persistence interface 302. A page
buffer 304 within the persistence layer 112 can store one or more
logical pages 306, and optionally can include shadow pages 311,
active pages 313, data pages of virtual files 315 and the like. The
logical pages 306 retained in the persistence layer 112 can be
written to a storage (e.g. a longer term storage, etc.) 114 via an
input/output component 116, which can be a software module, a
sub-system implemented in one or more of software and hardware, or
the like. The storage 114 can include one or more data volumes 310
where stored pages 312 are allocated at physical memory blocks.
[0019] In some implementations, the data storage application 104
can include a row store 303 and a column store 305. The row store
303 can comprise or be otherwise in communication with a page
manager 314 and/or a savepoint manager 316. The page manager 314
can communicate with a page management module 320 at the
persistence layer 112 that can include a free block manager 322
that monitors page status information 324, for example the status
of physical pages within the storage 114 and logical pages in the
persistence layer 112 (and optionally in the page buffer 304). The
savepoint manager 316 can communicate with a savepoint coordinator
326 at the persistence layer 204 to handle savepoints, which are
used to create a consistent persistent state of the database for
restart after a possible crash. The row store 303 can access the
persistence interface 302 via an absolute page API 307. The column
store 305 which can store columns in contiguous memory can access
the persistence interface 302 via a virtual file API 309.
[0020] In some implementations of a data storage application 104,
the page management module of the persistence layer 112 can
implement shadow paging. The free block manager 322 within the page
management module 320 can maintain the status of physical pages.
The page buffer 304 can included a fixed page status buffer that
operates as discussed herein. A converter component 340, which can
be part of or in communication with the page management module 320,
can be responsible for mapping between logical and physical pages
written to the storage 114. The converter 340 can maintain the
current mapping of logical pages to the corresponding physical
pages in a converter table 342. The converter 340 can maintain a
current mapping of logical pages 306 to the corresponding physical
pages in one or more converter tables 342. When a logical page 306
is read from storage 114, the storage page to be loaded can be
looked up from the one or more converter tables 342 using the
converter 340. When a logical page is written to storage 114 the
first time after a savepoint, a new free physical page is assigned
to the logical page. The free block manager 322 marks the new
physical page as "used" and the new mapping is stored in the one or
more converter tables 342.
[0021] The persistence layer 112 can ensure that changes made in
the data storage application 104 are durable and that the data
storage application 104 can be restored to a most recent committed
state after a restart. Writing data to the storage 114 need not be
synchronized with the end of the writing transaction. As such,
uncommitted changes can be written to disk and committed changes
may not yet be written to disk when a writing transaction is
finished. After a system crash, changes made by transactions that
were not finished can be rolled back. Changes occurring by already
committed transactions should not be lost in this process. A logger
component 344 can also be included to store the changes made to the
data of the data storage application in a linear log. The logger
component 344 can be used during recovery to replay operations
since a last savepoint to ensure that all operations are applied to
the data and that transactions with a logged "commit" record are
committed before rolling back still-open transactions at the end of
a recovery process.
[0022] With some data storage applications, writing data to a disk
is not necessarily synchronized with the end of the writing
transaction. Situations can occur in which uncommitted changes are
written to disk and while, at the same time, committed changes are
not yet written to disk when the writing transaction is finished.
After a system crash, changes made by transactions that were not
finished must be rolled back and changes by committed transaction
must not be lost.
[0023] To ensure that committed changes are not lost, redo log
information can be written by the logger component 344 whenever a
change is made. This information can be written to disk at latest
when the transaction ends. The log entries can be persisted in
separate log volumes 317 while normal data is written to data
volumes 310. With a redo log, committed changes can be restored
even if the corresponding data pages were not written to disk. For
undoing uncommitted changes, the persistence layer 112 can use a
combination of undo log entries (from one or more logs) and shadow
paging.
[0024] The persistence interface 302 can handle read and write
requests of stores (e.g., in-memory stores, etc.). The persistence
interface 302 can also provide write methods for writing data both
with logging and without logging. If the logged write operations
are used, the persistence interface 302 invokes the logger 344. In
addition, the logger 344 provides an interface that allows stores
(e.g., in-memory stores, etc.) to directly add log entries into a
log queue. The logger interface also provides methods to request
that log entries in the in-memory log queue are flushed to
disk.
[0025] Log entries contain a log sequence number, the type of the
log entry and the identifier of the transaction. Depending on the
operation type additional information is logged by the logger 344.
For an entry of type "update", for example, this would be the
identification of the affected record and the after image of the
modified data.
[0026] When the data application 104 is restarted, the log entries
need to be processed. To speed up this process the redo log is not
always processed from the beginning. Instead, as stated above,
savepoints can be periodically performed that write all changes to
disk that were made (e.g., in memory, etc.) since the last
savepoint. When starting up the system, only the logs created after
the last savepoint need to be processed. After the next backup
operation the old log entries before the savepoint position can be
removed.
[0027] When the logger 344 is invoked for writing log entries, it
does not immediately write to disk. Instead it can put the log
entries into a log queue in memory. The entries in the log queue
can be written to disk at the latest when the corresponding
transaction is finished (committed or aborted). To guarantee that
the committed changes are not lost, the commit operation is not
successfully finished before the corresponding log entries are
flushed to disk. Writing log queue entries to disk can also be
triggered by other events, for example when log queue pages are
full or when a savepoint is performed.
[0028] The column store 305 can persist its tables to virtual files
provided by the persistence layer 112 via the virtual file API 307.
Internally the persistence layer 112 can map a virtual file to a
chain of linked pages 315 stored in the page buffer 304. Data
belonging to one columnar table can be stored in multiple virtual
files: one virtual file per column for a main storage and one
virtual file for a delta log. In addition, one virtual file can
optionally be stored per column for the main storage of the history
part of the table, and/or one virtual file can optionally be stored
per table for the delta of the history part of the table. The
persistence layer 112 can maintain a directory that stores for each
virtual file the start page and additional information such as the
size and the type of the virtual file.
[0029] As stated above, virtual files can be used to store main and
delta parts of columnar tables. These files can be read on the
first access of the corresponding table into memory. With some
implementations, while read accesses happen only on the in-memory
representation of data, updates, appends, overwrites and truncates
can also be written to the virtual file on disk. After
partitioning/moving of a virtual file from a source node to a
destination node, the virtual file can be read into memory on first
access on the destination node. To support recovery from log
backup, moving a virtual file from one node to the other (if the
techniques described below are not incorporated) can either require
writing a redo log on the destination node for all
partitioned/moved data or explicit expensive synchronization of
recovery on several nodes, which is in both cases too big
performance penalty.
[0030] The content of a main storage can only change when a delta
merge operation is performed. Therefore the main virtual files can
only be written when a merge is done. Note that this does not mean
that main data is written to disk during a merge operation: when
the column store 305 writes to a virtual file, the data can be
written into the page buffer 304 of the persistence layer 112. It
is the responsibility of the persistence layer 112 to determine
when the data in the virtual file is actually flushed to disk
(e.g., during page replacement or at latest when the next savepoint
is written, etc.).
[0031] A delta merge operation is unique to the column store 305
and is not synchronized with the savepoints of the persistence
layer 112. Delta merge is primarily an optimization of in-memory
structures performed on the granularity of a single table. The
savepoint, on the other hand, works on the whole database and its
purpose is to persist changes to disk.
[0032] All changes executed on column store 305 data go into delta
storages in the data volumes 310. The delta storages can exist only
in memory as opposed to be written to disk. However, the column
store 305 can, via the logger 344, write a persisted delta log that
contains logical redo log entries for all operations executed on
the delta storages. Logical log, in this context, means that the
operation and its parameters are logged but no physical images are
stored. When a delta merge operation is executed, the changes in
the delta storage can be merged into the main storage and the delta
log virtual file can be truncated.
[0033] Despite of the name "delta log", the delta log virtual files
are not really logs from the persistence layer 112 point of view.
For the persistence layer 112 they are just data. The actual redo
log and undo entries can be written a log volume 317 in the
persistence layer 112. The virtual files used for delta logs can be
configured as logged. Whenever column store 305 writes to the delta
log virtual file, the persistence layer interface 302 invokes the
logger 344 and an undo manager to write redo log entries and undo
information. This ensures that the delta log virtual files can be
restored after a restart--just like any other data. After the delta
log virtual files are restored they are ready to be processed by
column store 305 to rebuild the in-memory delta storages from the
logical delta log entries.
[0034] During a delta merge operation the main files for the
affected table(s) can be rewritten and the delta log file can be
truncated. For all these operations no log is written by the
persistence layer 112. This is possible, because all operations
executed on the tables were already logged when the delta files
were written as part of the original change operation. The merge
operation does not change, create or delete any information in the
database. It is just a reorganization of the way existing
information is stored. To prevent that logs are written for a merge
operation, the virtual main files are configured as not logged and
a special not logged operation is used for delta log
truncation.
[0035] During restart, the persistence layer 112 can restore the
main virtual files from the last savepoint. The delta log virtual
files can be restored from the last savepoint and from the redo
log. When the persistence layer 112 has finished its part, the main
storage of the columns can be loaded from the virtual files into
column-store memory. This involves memory copy operations between
data cache in the page buffer 304 of the persistence layer 112 and
the contiguous memory areas in column store 305. The column store
305 can then execute the logical redo entries from delta log
virtual files and rebuild the in-memory delta storages.
[0036] As mentioned above, there is metadata that allows to define
for each columnar table whether it is to be loaded during system
startup. If a table is configured for loading on demand, the
restore sequence for that table is executed on first access.
[0037] In some situations, it can be necessary to partition data
within a virtual file among two or more nodes. With reference to
the diagram 400 of FIG. 4, a virtual file 414 on a source node 410
within a distributed data storage system can be partitioned by
creating a new file 424 (e.g., an empty object, etc.) on a
destination node 420 containing a special record 426 with (i) a
link to the original virtual file 414 on the source node 410; and
(ii) partitioning criteria 428 that characterizes a corresponding
partition on the original virtual file 414. This operation can be
logged by the logger 344. The original virtual file 414 can be kept
unchanged on the source node. When the virtual file is read on the
destination node, the link 426 is encountered which with the
partitioning criteria 428, in turn, results in the data from the
partition of the original virtual file 410 being accessed on the
source node 420. New data 430 can be appended after the link record
426 on the destination node 420, thus always all data of the file
can be read. As used in this context, nodes can refer to servers
having their own persistency.
[0038] When performing columnar table merge operation, virtual
files containing compressed data of a corresponding table can be
overwritten completely with the new version and the virtual file
for deltas will be truncated. These operations can automatically
overwrite the link 426 to the source node 410. During a link
cleanup operation after commit, the original files can be scheduled
for removal. After a savepoint on the destination node 420 has
persisted the new versions of the files to secondary storage, old
files on the source node 410 can be dropped (non-logged). At this
time, files can be completely moved to the destination node 420,
without unnecessary performance penalty by logging whole contents
on the destination node 420.
[0039] During recovery from log, link record 426 can be recovered
as well as all new data 430 appended to the file. The portion of
the old virtual file 414 corresponding to the partition on the
source node 410 can be kept because dropping of the virtual file
414 on the source node 410 need not be logged. If the portion of
the virtual file 414 corresponding to the partition is deleted
during recovery, the deletion can schedule dropping the portion of
the original file 414 corresponding to the partition on the source
node 410 after recovery ends. Otherwise, there would be a file 424
with the link 426 to old data on the source node 420 corresponding
to the partition (or even a chain of links, if the virtual file 414
has been moved several times).
[0040] The subject matter described above can be extended to enable
a virtual file to be repartitioned from n partitions to m
partitions and/or to join n partitions to a single partition. With
such variations, instead of writing a single link on each
destination node 420, several links can be written on the
destination node 420 which refer to all original n partitions where
to read the source data (which can be from a plurality of different
nodes). Such an arrangement can be further optimized if a new
partition of the source node 410 only a subset of the data of some
of the original partitions (e.g., previous partition criteria was
partition key module 2 while the new criteria is partition key
modulo 4, etc.).
[0041] Aspects of the subject matter described herein can be
embodied in systems, apparatus, methods, and/or articles depending
on the desired configuration. In particular, various
implementations of the subject matter described herein can be
realized in digital electronic circuitry, integrated circuitry,
specially designed application specific integrated circuits
(ASICs), computer hardware, firmware, software, and/or combinations
thereof. These various implementations can include implementation
in one or more computer programs that are executable and/or
interpretable on a programmable system including at least one
programmable processor, which can be special or general purpose,
coupled to receive data and instructions from, and to transmit data
and instructions to, a storage system, at least one input device,
and at least one output device.
[0042] These computer programs, which can also be referred to
programs, software, software applications, applications,
components, or code, include machine instructions for a
programmable processor, and can be implemented in a high-level
procedural and/or object-oriented programming language, and/or in
assembly/machine language. As used herein, the term
"machine-readable medium" refers to any computer program product,
apparatus and/or device, such as for example magnetic discs,
optical disks, memory, and Programmable Logic Devices (PLDs), used
to provide machine instructions and/or data to a programmable
processor, including a machine-readable medium that receives
machine instructions as a machine-readable signal. The term
"machine-readable signal" refers to any signal used to provide
machine instructions and/or data to a programmable processor. The
machine-readable medium can store such machine instructions
non-transitorily, such as for example as would a non-transient
solid state memory or a magnetic hard drive or any equivalent
storage medium. The machine-readable medium can alternatively or
additionally store such machine instructions in a transient manner,
such as for example as would a processor cache or other random
access memory associated with one or more physical processor
cores.
[0043] The subject matter described herein can be implemented in a
computing system that includes a back-end component, such as for
example one or more data servers, or that includes a middleware
component, such as for example one or more application servers, or
that includes a front-end component, such as for example one or
more client computers having a graphical user interface or a Web
browser through which a user can interact with an implementation of
the subject matter described herein, or any combination of such
back-end, middleware, or front-end components. A client and server
are generally, but not exclusively, remote from each other and
typically interact through a communication network, although the
components of the system can be interconnected by any form or
medium of digital data communication. Examples of communication
networks include, but are not limited to, a local area network
("LAN"), a wide area network ("WAN"), and the Internet. The
relationship of client and server arises by virtue of computer
programs running on the respective computers and having a
client-server relationship to each other.
[0044] The implementations set forth in the foregoing description
do not represent all implementations consistent with the subject
matter described herein. Instead, they are merely some examples
consistent with aspects related to the described subject matter.
Although a few variations have been described in detail herein,
other modifications or additions are possible. In particular,
further features and/or variations can be provided in addition to
those set forth herein. For example, the implementations described
above can be directed to various combinations and sub-combinations
of the disclosed features and/or combinations and sub-combinations
of one or more features further to those disclosed herein. In
addition, the logic flows depicted in the accompanying figures
and/or described herein do not necessarily require the particular
order shown, or sequential order, to achieve desirable results. The
scope of the following claims may include other implementations or
embodiments.
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